Liquid crystal display elements and touch panels are used in large electronic apparatuses such as personal computers and televisions, small electronic apparatuses such as car navigation systems, mobile phones, and electronic dictionaries, and display devices for OA and FA apparatuses. In these liquid crystal display elements and touch panels, transparent conductive films are used in part of wirings and pixel electrodes or terminals, which should be transparent. Moreover, transparent conductive films are also used in devices such as solar cells and lightings.
Conventionally, indium oxide tin (ITO), indium oxide, and tin oxide are used as a material for a transparent conductive film because these materials exhibit high transmittance to visible light. Electrodes disposed on substrates for a liquid crystal display element are mainly those having patterned transparent conductive films composed of the above materials.
A method of patterning a transparent conductive film is usually the method of forming a transparent conductive film on a base material such as a substrate, then forming a resist pattern by photolithography, and removing a predetermined portion of the conductive film by wet etching to form a conductive pattern. In the cases of ITO films and indium oxide films, a mixed solution composed of two solutions of hydrochloric acid and ferric chloride is often used as the etching solution.
Although ITO films and tin oxide films are usually formed by sputtering, the properties of transparent conductive films are readily fluctuated according to the difference in the type of sputtering, the power of sputtering, the pressure of the gas, the temperature of the substrate, and the type of the atmosphere gas. Such a fluctuation in film quality of transparent conductive films caused by a variation in sputtering conditions causes a fluctuation in the etching rate during wet etching of the transparent conductive films, readily reducing the yields of products due to failed patterns. Moreover, the conductive pattern formation method comprises a sputtering step, a resist forming step, and an etching step; these steps require long time, and place a great burden in view of cost.
To solve the above problems, attempts to form transparent conductive patterns using a material other than ITO, indium oxide, and tin oxide have been performed recently. For example, Patent Literature 1 below discloses a conductive pattern formation method of forming a conductive layer containing conductive fibers such as silver fibers on a substrate, then forming a photosensitive resin layer on the conductive layer, and exposing the photosensitive resin layer from thereabove through a patterning mask to develop a pattern.
Patent Literature 2 discloses a method of using a conductive film for transfer comprising at least a peelable conductive layer disposed on a support and an adhesive layer disposed on the conductive layer, and bonding the conductive layer to a substrate through the adhesive layer, and also discloses optional patterning of the conductive layer after transfer.
Patent Literature 3 discloses a method of forming a conductive pattern by a method of using a photosensitive conductive film comprising a conductive layer disposed on a support film and a photosensitive resin layer disposed on the conductive layer, and laminating the photosensitive resin layer on a substrate so as to closely bond to the substrate.